A 25-year-old G1 P0 with non-contributive family and personal history was referred to our center at 24 weeks and 30 weeks of gestation. We found Blake’s pouch cyst. No other abnormalities were detected.

The baby boy was born at term, weight of 3500 gr, height of 53 cm, Apgar 7/9 with no neurological symptoms. At the age of 3 months, MRI was performed and confirmed the diagnosis. The child develops without neurological disease.

Blake's pouch cyst (BPC) has been considered a pathological entity deriving from abnormal development of the posterior membranous area of the fetal brain. This pathology is characterized by normal anatomy and size of the vermis; mild/moderate anti-clockwise rotation of the vermis; normal size of the cisterna magna.

Image 1: 24 weeks. Normal profile of fetus

Image 2: 24 weeks. Normal appearance of cerebellum in the upper part

Image 3, 4: Abnormal appearance of the cerebellum in the lower part (the classic keyhole sign) at 24 and 30 weeks

Image 7, 8: 3D and Multiplanar three-dimensional (3D) ultrasound was used to enhance the assessment of the Blake's pouch cyst and its relationships with the vermis and the posterior fossa. The image showed septum pellucidum (1),corpus calosum (2); Thalamus(3);Vermis cerebellum (rotation); Fourth ventricle is open(4); the Blake's pouch cyst (5)